Example 24, Injection Mold for an Angle Fitting from Polypropylene

Previous Page 90 Examples ~ Example 24/Example 25 Example 24, Injection Mold for an Angle Fitting from Polypropylene If ejectors are located behind movable side cores or slides, the ejector plate return safety checks whether the ejectors have been returned to the molding position If this is not the case, the molding cycle is interrupted This safety requires a switch on the mold that is actuated when the ejector plate is in the retracted position The ejector plate return safety thus h c tions only if the molding cycle utilizes platen preposition, i.e., after the molded parts have been ejected, the clamping unit closes to the point at which the ejector plate is returned to the molding position by spring force Only then does the control system issue the “close mold” command In molds requiring a long ejector stroke, spring return of the ejector plate is often not sure enough For such cases, there is an ejector return mechanism that hlfills this h c t i o n Attachment of the ejector plate return safety is shown in Figs to This single-cavity mold is used to produce an angle fitting (1) Two long side cores (2) meet at an angle of 90” The somewhat shorter side core is pulled by a cam pin (3), while the longer core is pulled by a slide (4) The difficulty is that blade ejectors (5) are located under the two cores and must be returned to the molding position after having ejected the finished part before the two cores are set as the mold closes and possibly damage the blade ejectors Possible consequences include not only broken blade ejectors but also a damaged cavity Either of these could result in a lengthy interruption of production For this reason, a helical spring (6) that permits operation with platen preposition is placed on the ejector rod This spring then returns the ejector plate To ensure proper operation, a microswitch (7) is mounted to the clamping plate (S), while a pin (10) that actuates the switch is mounted in the ejector plate (9) After connecting the cable with the switch housing of the movable clamping plate, the ejector plate return safety is complete Example 25, Mold for Bushings from Polyamide with Concealed Gating A flanged bushing is to be injection molded in such a way that any remnants of the gate are concealed or as inconspicuous as possible The bushing would normally require a two-plate mold with a single parting line The molded part would then be released and ejected along its axis, which coincides with the opening direction of the mold The gate would be located on the outer surface of the flange since it is in contact with the mold parting line In order to satisfy the requirement for an “invisible” gate, the cavities (two rows of four) are placed between slides carrying the cores (Fig 1) even though there are no undercuts From a central sprue the melt flows through conical runners in the cores to pinpoint gates located on the inner surface of the bushings As the slides move during opening of the mold the gates are cleanly sheared off flush with the adjacent part surface The flexibility of the plastic selected is sufficient to permit release of the end of the runner from the angled runner channel The parts are now free and can drop out of the mold 11 12 ’ io Figure Mold for bushings with concealed gating 1: stationay-side clamping plate; 2: stationary-side backing plate; 3: wedge; 4: slide; : movable-side backing plate; 6: injection-side cavity half; 7: ejector-side cavity half; 8: core; 9: spme bushing; 10: locating ring; 11: part ejector; 12: sprue ejector (Courtesy: Erikssons Verktygsindustri, Gislaved/Sweden) Example 26: Injection Mold for the Valve Housing of a Water-Mixing Tap Made from Polyacetal 91 Example - 26, Injection Mold for the Valve Housing of a Water-Mixing Tap Made from Polyacetal Avalve housing (Figs and 2) had to be designed and produced for a water-mixing tap The problem when designing the tool (Figs to 7) resulted from the undercuts in four directions Originally occurring considerable differences in wall thicknesses have been eliminated during optimization Demands for high precision of the cylindrical valve seat in Figure View of the interior of the valve housing, showing the places of core penetration Company photo: ARCU, Altemo/Sweden Figure View of the exterior of the valve housing Company photo: ARCU, Altemo/Sweden particular were negatively influenced by various recesses in the wall and adjoining partitions, which favored sink marks and ovalness Polyacetal (POM) had been chosen as molding material The complete molded part had to have homogeneous walls, and be free from flow lines if at all possible, as it would be subjected to everchanging contact with hot and cold water during an estimated long life span Inadequately hsed weld lines would be capable of developing into weak spots and were therefore to be avoided at all cost Provision has been made for an electrically heated spme bushing (30) (Fig 6) in order to avoid a long spme The resultant very short runner leads to the gate on the edge of the pipelike housing, to be hidden by a part that is subsequently fitted to cover it Two cores each cross in the pipe-shaped housing, i.e one core (16) each penetrates another core (1 9) This obviously presents a danger spot should the minutest deviation occur from the specified timeand movement-based coordination as well as from the accuracy in the mold The hollow cores (19) are kept in position by mechanical delay during the first phase of mold opening, while the crossing cores (16) are each withdrawn by an angle pin (31, 32) Mechanical actuation has been preferred over a hydraulic or pneumatic one in this case in order to exclude the danger of a sequencing error (the so-called human factor) during set-up and operation The cores (16, 33) consist of a copper-beryllium alloy They are cooled by heat conducting pins (27, 28) 3 Figures to Injection mold for the valve housing of a water-mixing tap 1, 2, 3, 4: O-rings; 5, 6, 7: core clamping rings; 8, 9: core retainer with angle pin hole; 10: core retainer with angle guide; 11, 12: wedge; 13: guide rail; 14, 15: guide plate for core retainer; 16: internal core; 17, 18: external core; 19: core; 20: upper mold cavity half; 21: lower mold cavity half; 23: insert; 25: angle guide; 26: core baffle; 27, 28, 29: heat conducting pins; 30: heated spme bushing; 31, 32: angle pins; 33: support core; 34, 35: ejector; 36: spme ejector; 37: return pin; 38: locating ring; 38, 40, 41: stop; 43: screw; 44: lock nut; 45: fixed mold plate; 46: retainer plate for the upper mold cavity; 47: temperature control medium connection; 48: lower mold cavity retainer plate; 49: moving mold plate (Courtesy: Seveko Fristedt & Sundberg, Karlskrona/Sweden, and Gustavsson Gravyr, Stockholm) Examples ~ Example 26 I4a 31- B-B Fig 17 ? f i A-A 35 34 Fig 92 Fig 23 Fie ! c-c Fig I 49 Example 27: Mold for a Lid with Three Threads Made from Polyacetal 93 Example 27, Mold for a Lid with Three Threads Made from Polyacetal The lid is a rotationally symmetrical part with three threads Threads I and I1 are of the same pitch and can be formed by a single threaded core The material employed is polyacetal The total number of units to be produced is small The mold (Figs to 5) is of simple design The external shape of the molded part is formed by an insert (c), which is housed in mold plate (b) and secured against rotating The temperature of this insert is controlled via a ring channel (heating/cooling system A) Thread I11 is formed by two slides (d) The part is injected through a diaphragm gate (e) The internal shape of the lid is obtained from a main core cf), which is housed in the mold plate ( p ) and is secured against rotating The temperature of this core is controlled via an internal tube (heating/cooling system B) Its effectiveness is increased by the soldered-on spiral (g) The threads I and I1 are formed by a single threaded core (h) Because of the low number of moldings required, the mold has been designed for the threaded core (h) to be unscrewed outside the tool The threaded core is inserted into an ejector ring (i) and is retained by three springloaded detents (k) It is located by the cone ( I ) of the fixed core cf) The mold opens at parting plane 1-1 positively assisted by two latches (m) The threadforming slides (d) are moved outward by this action After a distance of 18 mm the latches are released by the control strips (n) and the mold opens at the main parting plane 11-11 By actuation of the machine ejector the threaded core (h) is pushed in the direction of the fixed half by three ejector pins (0) and the ejector ring (i) for a distance of 90mm (height of the molding plus 10mm) During the movement the threaded core strips the molding off the fixed core cf) Then the molded part, with the threaded core (h), is pulled manually out of the stripping ring (i) without any danger of damaging the fixed main core cf) Unscrewing takes place outside the mold with the aid of an unscrewing device To shorten the cycle time, several temperature controlled threaded cores are employed While one part is being unscrewed, the next molded part is being produced r A-! I Fig Fig B C 326 Fig D-E D 94 Fig A Examples ~ Example 27 p Fig F- G Figures to Mold for lid with three threads a: molded part; : cavity plate; c: insert; d : slides; e : diaphragm gate; f : main core; g : spiral; h : threaded core; i: ejector ring; k : springloaded detent; I : core; m: latch; n: control strip; 0:ejector pin; p : mold cavity plate I, 11, 111: threads g7h * b I B3C I 95 Example 28: Two-Cavity Injection Mold for Coupling Sleeves Made from Polyamide Example 28, Two-Cavity Injection Mold for Coupling Sleeves Made from Polyamide b m v -w- Figures to 12 Two-cavity unscrewing mold for coupling sleeve 1: arrangement of mold cavities; 2: coupling sleeve; 3: fixed mold half; 4: fixed core for central hole in the molding; 5: moving core for the central hole in the molding; 6: locator for the screw cores; 7: M 10 thread on the threaded core; 8: threaded core guide; 9: threaded core pinion t = 15; 10: lead thread on the threaded core; 11: guide bushing; 12, 13: rack; 14: hydraulic cylinder; 15, 16: electric switches; 17: tunnel gate; 18: runner; 19: nozzle on the machine; 20: berylliumcopper nozzle tip; 21: ejector; 22: ejector plates; 23: ejector pins; 24: push-back pins; 25: support pillars; 26: insulating plate E : cores to be operated independently of each other, so that they can be driven by one rack each To avoid M h e r core pulls for the remaining shape of the molded part, it is put perpendicularly into the parting line of the mold by its axis of symmetry Concerning direct operation of the threaded cores by racks, a check must be made to ascertain that adequate transmission can be achieved or if intermediate stages are required to avoid an excessively long rack stroke The pitch of the metric thread M 10 is h = 1.5mm Allowing for a certain safety, an unscrewing distance of 11 mm must be taken up, which results in 1111.5= 7.33 rotations of the threaded core For a Figures to PA 66 coupling sleeve containing 30% by weight of glass fiber reinforcement The coupling sleeve in Figs to had to be produced in a PA 66 with 30% by weight glass fiber reinforcement The injection molded part has a center hole, entered by tapped M 10 holes that, starting from the peripheral surface, are opposite each other As set screws are screwed into each tapped hole to push against a centrally fitted shaft, it is not necessary to have a continuous thread in both holes, which would have called for a bridging threaded core that would have had to cross the center core Apart from problems with sealing, the unscrewing device also would have caused difficulty, as it would have had to perform a larger stroke Use of the molded part allows for two separate threaded f - b m ,-I ah E I N 96 Examples ~ Example 28 W N U W I W Example 29: Injection Mold for the Housing of a Polypropylene Vegetable Dicer pitch circle diameter of = 12 mm and a modulus of rn=O.Smm, the pinion of the threaded core works out at t = 12/0.8 = 15 teeth and a pitch circle circumference of 12 x 7c = 37.68mm For 7.33 turns this results in a required rack stroke of 7.33 x 37.68 = 276.19 111111 Standard hydraulic cylinders of 280mm stroke are available Divided by the pitch d = 7c x m = 2.5 mm of the gear tooth system, this corresponds to 112 teeth on the rack, which with 15 teeth on the pinion turns the latter 7.46 times during one stroke From this results an unscrewing distance of 11.19mm, which is sufficient It must be checked whether the space available on the injection molding machine allows installation of the mounting hardware and the hydraulic cylinder under the mold The mold design (Figs to 12) is such that two sleeves (1) can be produced at the same time The unscrewing equipment has been installed in the fixed mold half (3) so that the hydraulic cylinder (14) does not have to participate in the opening and closing movement but can remain in position The center bore of the coupling, which tapers toward the moving mold half, is formed by two cores (4) and (5) which are self-centering The locators (6) for the threaded cores enter the core (4), which is held in the stationary side of the clamping plate, from both sides The threaded cores are made up of the locators (6), the M 10 thread (7), a guide (8), the 15 gear teeth (9), and the guide thread (10) at the other end, which runs in the fixed 97 guide bushing (11) The two racks (12) and (13) have been arranged offset to each other so that opposite directions of rotation can be transmitted to the opposing threaded cores The hydraulic cylinder pushes the racks (12) and (13) up to unscrew the threaded cores The upper racks protrude from the mold and need to be guarded by a screen For interlocking with the machine’s control circuit for the cycle sequence, the racks contact switch (15) in the lower and switch (16) in the upper position By employing lateral submarine gating (17), the coupling sleeves are automatically degated from the runner (18) This is fed directly through a berylliumcopper nozzle tip (20), which is screwed into the female thread of the nozzle on the machine (19) to avoid the conventional tapered sprue penetrating the fixed mold half (3) The operating sequence of the unscrewing mold takes place as follows: The racks are moved in by the hydraulic cylinders, unscrewing the threaded cores from the molded parts Then the opening movement of the mold starts When finished, the hydraulic ejector of the machine, to which the ejector bar is coupled (21), pushes forward the ejector plates (22) and through them the ejector pins (23) for the coupling sleeves and runner For safety, the push-back pins (24) also move out simultaneously They have to return the ejector plate to the starting position in any case when the mold closes Once the mold is closed, the racks are pulled up again and the new cycle can start with injection Example 29, Injection Mold for the Housing of a Polypropylene Vegetable Dicer Molded Part The housing accommodates a cutting disc that is driven by a hand crank (Fig 1) The shaft of the crank drive is located in a bore in the housing The underneath of the housing has a recess for accommodating a suction cap to attach the device to a table The top of the housing has a filling shaft which supplies the cutting disc with the vegetables to be diced A feed hopper will be attached to this filling shaft The molded part weighs 386g Figure Housing for a polypropylene vegetable dicer 98 Examples Example 29 ~ 13 12 / LB 1L 15 16 Figure Longitudinal section through the injection mold for the housing 1: ejector retaining plate; 2: ejector base plate; 3: cylinder pin; 4: ejector pin; 5: locating ring; 6: stop plate; 7: ejector rod; 8: core pin; 9: ejector sleeve; 10: locating pin; 11: screw; 12: return pin; 13: guide pillar; 14: guide bushing; 15: support plate; 16: buffer pin; 17: mold insert; 18: punch; 19: locating pin; 20: sprue bushing; 21: punch; 22: punch retaining plate; 23: slides; 24: angle pin; 25: adjusting plate; 26: wedge: 27: mold plate (nozzle side); 28: split shoulder; 29: cooling pipe; 30: mold plate (clamping side); 31: adjusting plate; 47: bar; 48: mounting plate I L? Mold The mold was designed so that the dicing chamber lies in the mold-opening direction The housing base, the filling shaft and two other apertures are ejected with the aid of splits, a core puller and slides (Figs and 5) The slide (23), moved by the angle pin (24), forms the inside contour of the housing base (Fig 2) In the closed position, the split shoulder (28) lies against punch (21) and so forms the bore for attaching the suction cap to the housing base The cylindrical slide lies in the mold parting line and each half is Figure Guiding of mold slides in Fig 50: guide bar enclosed by the mold plates (27) and (30) Guide strips (50) (Fig 3) lead the slide on the mold plate (30) The slide supports itself against the effect of the cavity pressure via the adjusting plate (25) and the wedge (26) Bending of the wedge is prevented by the adjusting plate (31) and the mold plate (30) The vegetable filling shaft and the passage to the dicing chamber are formed by the mobile core (33) (Fig 6) Its movement is provided by the angle pin (32) Figure shows the core guide in the guide strip (45) The inserted core is locked via the wedge (35) and adjusting plate (34) The guide strip (37) (Fig 8) forms a rectangular opening in the side wall of the housing which lies half over and half under the mold parting line It is moved by two angle pins (38) and is locked in the closed state by two bolts (39) A guide strip (49) which is bolted and doweled to the mold plate (30) is guided in a T-slot (Fig 9) Finally, a slit has to be formed in the housing wall that penetrates a reinforcement there Rectangular aperture and reinforcement are formed by the slide (40) (Fig 10) which is actuated by the angle pin (41) and locked by the wedge (42) Two bars (51) (Fig 11) serve to guide the slide on the mold plate (30) Example 29: Injection Mold for the Housing of a Polypropylene Vegetable Dicer B Figure View of the moving side of the injection mold for a PP housing Since the angle pins traverse out from the slide, the core and the guide bars on mold opening, each is provided with ball catches that keep these guide elements in the “open” position Bars (47) and rolls (43) support the plate (15) on the clamp plate (48) D 99 F Figure View of the stationary side of the injection mold for a PP housing Part Release/Ejection On opening, the angle Pins on the fixed side push the splits, cores and slides on the 32 33 34 35 Runner System/Gating The spme bushing (20) lies on the axis of the housing bore, which accommodates the blade drive shaft The end of the spme bushing forms the face of an eye inside the dicing chamber that is a part of the crankshaft mount A core pin (8) protrudes into the bore of the spme bushing and divides the spme into three pinpoint gates Mold Temperature Control The coolant is guided in bores and cooling channels in the mold plates, inserts and punches The splits (23) and (33) Offer sufficient space for modating cooling channels (33) Figure Demolding of the feed in a vegetable dicer 32 angle pm, 33 core, 34 adjusting plate, 35 wedge, 36 msert 100 Examples Fig ~ Example 29 Fig Fig Fig 10 Fig 11 9-D J-J K-K G-G L L9 51 H-H 1-1 LO LL 15 16 37 36 36 L1 12 Figure Slide guide for Fig 49: guide bar Figure Core guiding for Fig 44: punch; 45: guide bar; 46: punch Figure 10 Demolding a slot 30: slide; 41 angle pin; 42: wedge Figure Demolding the rectangular aperture 37: slide; 38: angle pin; 39: locking bolt Figure 11 Slide guide for Fig 10 51: guide bar (Courtesy: Plastor p.A., Oradea/Romania) moving side so far outward that they release the undercuts of the housing The molded part remains on the moving mold side Ejector pins (4) and ejector sleeve (9) push the molded part out of the ejector-side mold cavities and off core pin (8) Since the ejector pins are contour-forming, they must be secured against twisting (pin 3) On mold closing, the ejector system is brought into the injection molding position by ejector-plate return pins (12) and buffer pins (16), and so too are the splits, cores and slides by their respective angle pins Example 30: Two-Cavity Injection Mold for a Polypropylene Toy Tennis Racket 101 Example - 30, Two-Cavity Injection Mold for a Polypropylene Toy Tennis Racket The toy tennis racket shown in Fig measures 220mm x 520mm and is made of polypropylene Handle and frame are extensively ribbed to provide stability, and the playing face also consists of a network of ribs The handle is partly hollow The bore in the handle is sealed with a plug Simple Die Design The mold with the mold-fixing dimensions 700mm x 480mm is a two-part design (Fig 2) This means that, under the influence of the mold buoyancy, stress is applied uniformly on the clamping unit of the injection molding machine, and that the gate is positioned in a favorable, materialsaving location The maximum mold height is 280 mm Cavity plates (18, 19) with attached handle inserts (36) lie on both sides of the mold parting line The tips of the core slides (3) project into the hollows formed by the handle inserts The core slides can be moved on T-shaped guide plates (6) and guide bars (7) parallel to the mold parting line The ejector bars (37) are bolted to the guide plates (6) These are guided in bushings (38) and they bear two ejector plates (23, 24) The angle pins (4) actuate the two core slides (3) on mold opening and closing They are locked in the injection position by wedge plates (1) In the open position, the ball catches (40) secure the core slides against unintentional movement Rolls (26) brace the plate (20) against the ejector-side clamp plate (22) The part-forming surface in the cavity plate and in the handle inserts are produced by spark erosion Operation of the Mold Figure Injection molded, polypropylene toy tennis racket The cavity wall temperature is 50 to 90°C (122 to 194°F) For ejection, the core slides (3) are partly pulled out of the handle bores of the rackets by the angle pins on mold opening (4) The force of the springs (33) is greater than the force exerted on the slides by the angle pin in the mold-opening direction, with the result that the guide plates (6) with their core slides (3) not lift away from the guide bars (7) in the cavity plate (19) The core slides therefore initially keep the two molded parts on the ejector side and pull them from the cavity plate on the feed side (18) Spmes and runners also remain in the moving mold half because of the undercut in the guide bushing for the spme ejector pin (25) After 60mm of the mold opening stroke, the core slides (3) have moved outward by around 25 mm and stopped The mold opens M e r till the ejector rod (30) meets the machine end stop The two ejector plates (23, 24) now eject the molded part via ejector pins (12, 25) out of the ejector-side mold cavities and eject the spme At the same time, the guide plates (6) are lifted out (3) from the cavity plate (19) with the core slides The molded parts now sitting loosely on the slide lobes can be removed by hand This process compresses the springs (33) further The springs (33) ensure during mold closing that core slide and ejectors get into the injection position before the mold closes completely The ejector-plate return pins (31) secure the stop position of the ejector mechanism With this mold, toy rackets can be produced with relatively little mold outlay However, an operator is required because the molded parts are removed manually from the injection molding machine 102 Examples ~ Example 30 C B-6 a 10 11 29 28 12 27 26 25 13 14 24 23 15 16 22 21 20 19 18 17 Figure Two-cavity injection mold for making the racket shown in Fig 1: wedge plate; 2: screw; 3: core slide; 4: angle pin; 5: screw; 6: guide plate; 7: guide bars; 8: buffer pin; 9: spme bushing; 10: locating pin; 11: screw; 12: ejector pin; 13: locating pin; 14: screw; 15: guide bushing; 16: guide pillar; 17: mounting plate; 18, 19: mold cavity plate; 20: plate; 21: spacer plate; 22: mounting plate; 23: ejector retaining plate; 24: ejector plate; 25: spme-ejector pin; 26: support roll; 27: screw; 28: locating ring; 29: guide bar; 30: ejector rod; 31: return pin; 32: ejector pin; 33: helical spring; 34: locating pin; 35: screw; 36: handle inserts; 37: ejector bar; 38: guide bushing; 39: screw; 40: ball catch; 41: cooling connection (Courtesy: Plastor p.A., Oradea/Romania) Example 31: Two Injection Molds with Two-step Ejection Process for Housing Components from Polycarbonate 103 Example 31, Two Injection Molds with Two-step Ejection Process for Housing Components from Polycarbonate Injection molds and pressure die-casting molds, depending on the type of gate and the shape of the molded article, sometimes require a multi-step ejection process in which individual ejection elements have a different stroke in order to safely release the molded article (molded parts plus gate) from the mold This is commonly achieved by employing mechanically controlled devices which, in conjunction with additional ejection plates, facilitate this releasing process The hydromechanical ejector accelerator described in this context allows a particularly simple mold design while requiring little effort in terms of assembly Figure shows its structure as well as its h c t i o n The ejector accelerator (1) as well as the ejector pin (4) are inserted into the two ejection plates (2, 3) Part (1) also receives the ejector pin (5) The ejection plates (2) and (3) are actuated by the ejector bolt (6) A stroke H1 is available for the ejection plates Activating the ejector bolt (6) initially gives rise to an equal forward motion of ejector pins (4) and (5), until after a stroke H2 the annular piston (7) of the ejector accelerator (1) strikes against the stopping face (8) (Fig 1B) Once the ejection plates (2, ~ A) ~ 6) 3) are moving fiuther, the annular piston (7) is being pressed into the oil chamber (9), where it replaces the existing hydraulic oil As a result, the central piston (10) dissociates from its piston stop (1) By the end of stroke H1 of the ejection plates (2, 3), the ejector pin (5) in the central piston (10) has passed a distance exceeding that of the ejector pin (4) by a distance H (Fig 1C) When the ejection plates are retracted, the restoring springs (12, 13) are pushing the central piston (10) and the annular piston (7) and therefore also the ejector pin (5) back into their original position The ejector accelerator is available in two sizes (Table 1) The size version can receive ejector pins with a tip diameter of up to mm and a tip height of up to mm; the corresponding tip sizes for the size version are 12 mm in diameter and 10 mm in height, respectively Application in Injection Molding of Caps Figure shows the application example of a double cap mold The two molded parts are injected sideways via a spme gate with a runner and tunnel gates (1) C) Figure Hydromechanical ejector accelerators 1: ejector accelerator; 2, 3: ejection plates; 4, 5: ejection pins; 6: ejector bolt; 7: annular piston; 8: stopping face; 9: oil chamber; 10: central piston; 11: piston stop; 12, 13: restoring springs A: ejector accelerator prior to ejecting; B: end of the synchronous movement of the ejector pins , and beginning of the advance of pin 5; C: end of the ejection process (Courtesy: Kiihner Industrievertretungen GmbH, Reutlingen, Germany) 104 Examples ~ Example Table Measures for the hydromechanical ejection accelerators TYP A H B F1 FN Ejection force Ejection/accelerator force L L1 L2 size 1 6,O 8,4 70,O 33,5 28,5 size 2 8,0 L3 L4 K D D1 7,O 15,4 8,0 23,O 26,O 12,5 105,5 52,5 41,O 11 24,O 12,O 40,O 44,O G T - - M8 F1 FN 175N 210N 15 370N 430N u I Figure Two-cavity die for injection molding of caps : spme; 2: stripper plate; 3: spme ejector pin; 4: ejector accelerator; : ejector bolt; 6, 7: ejection plates Example 31: Two Injection Molds with Two-step Ejection Process for Housing Components from Polycarbonate A pusher plate (2) is used to push the caps off the cores; this pusher plate also contains the runner and the boring for the gate extractor spigot When the mold is opened, the molded articles are being pulled out of their die cavities while the spme is being pulled out of the spme bush; the tunnel gate points are being severed and the spme is snapped off the tunnel borings When the pusher plate (2) subsequently moves to the right, the caps dissociate from the cores and may fall off The additional pusher stroke of the gate ejector (3) that is required to throw the spme off the pusher plate (2) is provided by the ejector accelerator (4) In this example, the ejector accelerator (4) is mounted in the center of the mold The ejector bolt (5) is positioned in a thread boring on the bottom of the ejector accelerator which receives the two ejection plates (6) and (7) .and of Casing Parts The mold shown in Fig is used to manufacture casing parts which have projecting parts or undercuts along their edges These are molded with the shaped pins (1, 2) The shaped pins (1, 2), the spme ejector pin (3), the return pins (4), and the ejector accelerators (5) are mounted in the ejection plates (6, 7) During ejection, the shaped pins and the ejector accelerators initially push the parts away from the cores The flatter casing part (on the left-hand side 105 inside the mold), however, still adheres to the shaped pins for a while but is finally pressed out of these The left-hand side of the photograph viewing the cavities from above (Fig 3, below) demonstrates that three ejector accelerators are required for this purpose Using only one or two ejector accelerators would cause tilting, so that one side of the casing part could get caught Only the arrangement in one plane (triangle) avoids this danger Release from the mold is therefore accelerated, since this technique obviates the need for the commonly used but time-consuming method of ejector jolting A coil spring (8) is sticking on the return pin (4); this coil spring enters a boring (9) as the ejector sheets are moving forward This has the following reason: Table lists two forces F1 and FN for each of the two ejector accelerator sizes These are the forces exerted by the ejector accelerator immediately after touching the stopping face (8) (Fig 1) or after a complete stroke of the ejection plates These forces are effective even if there are no molded articles for the ejector pins (4, 5) to push (Fig 1) If as in this case the ejector accelerators are positioned unsymmetrically relative to the ejector bolt (10) (Fig 3), then an overturning moment is created, which may cause jamming of the ejection plates in their guideways This overturning moment is almost entirely compensated by the two springs (8) sitting on the two return pins (4) opposite the ejector accelerators ~ ~ 106 Examples ~ Example 1- Figure Single injection mold for the upper and lower part of a casing made of polycarbonate A: section; B: section turned by 90"; C: top view 1, 2: shaped pin; 3: spme ejector pin; 4: return pin; : ejector accelerator; 6, 7: ejection plates; 8: coil spring; 9: boring; 10: ejector bolt (Courtesy: Roth Plastik & Form, Balingen-Weilstetten,Germany) C) Example 32: Injection Mold for a Polypropylene Container with a Threaded Neck 107 Example 32, Injection Mold for a Polypropylene Container with a Threaded Neck This is the description of a three-plate injection mold for a polypropylene container that does not show in the visual range any witness lines from slides Spme and ejectors are designed for automatic operation Specifications When the development of a household appliance had been concluded, the task of constructing a tool for the container of the appliance arose A molded part drawing served as the basis on which the geometrical shape, dimensions, permissible tolerances and polypropylene as material had been firmly established The container concerned is a largely rotationally symmetrical high-quality molded part with relatively high demands on the surface, on dimensional accuracy (required for assembly and operation) and on the mechanical loading of the polypropylene Feasibility of automatic production without postmolding finishing of the gate area Temperature Control Uniform mold temperature control to 50°C (122°F) is necessary to satisfy the quality requirements Effective temperature control had also been asked for in order to achieve short cycle times The mold was therefore equipped with five temperature control systems TS, independent of one another: System 1: Temperature control for the main core ( k ) System 2: Temperature control for the cavity (insert) (I System 4: Temperature control for the threadforming slides (c) System 5: Temperature control for the contourforming spme bushing (m) and the auxiliary core (n) The effectiveness of temperature control in the auxiliary core is increased by a copper pin (0) + Mold Design The design shown in Figs to is a three-plate mold (parting line I and 11) with stripper plate ( p ) When the injection molding machine opens, the mold is forced to open at I by the latches (b) Through this movement the two thread-forming slides (c)are pulled out of the thread by the cam pins (d), thereby releasing the undercuts formed by the thread The latches are guided by the cam strips (e) and they release after 28mm of travel Mold plate cf) stops The mold opens in the main parting line (11) The cavity retainer plate is guided by four additional guide pins (g) This plate is secured by end-stops (h) Runner System The melt is fed into the cavity via spme, conventional runners and gates (i) Despite the relatively high wall thickness of the molded part (3.5mm) attempts were successfully made to inject via four submarine gates (i) of 1.8mm diameter each The gates are sheared off during mold opening (I) The gates are in the upper mold cavity The choice of this gating system and its position offer the following advantages: Central gating This ensures even mold filling Position of the gate is outside the hctional and visible areas of the molded part ~ ~ Ejector Systems The molded part is stripped off the core by the stripper plate ( p ) This movement is effected by a hydraulically operated ejector on the machine The stroke of the ejector plate ( p ) is limited by two bolts (4) with end stops (r) The molding bead (s) in the ejector plate could cause it to stick on demolding For that reason the air blast ( t ) has been provided, which is charged with compressed air at the end of the ejection process This ensures certain discharge of the molded part The spme is pushed out of the retaining undercut and ejected by a separate ejector system (u) The movement of this ejector is actuated by contact of the bolt head (v) This bolt serves to couple the machine ejector with the ejector plate (w) Materials Used in the Mold The following materials were chosen for the individual parts of the mold: Part-forming inserts: case-hardening steel, case hardened Cavity retainer plate and stripper plate: nitrided annealed steel Mold base: tool steel, unalloyed ~ ~ ~ 108 Examples ~ Example 32 Figures to Injection mold for container with threaded neck I, 11: parting lines, TS to temperature control systems a: molded part; : latches; c: slides; d : cam pins; e: guide cams;f: cavity retainer plate; g : guide pins; h: end stops for cavity retainer plate, f ; i: submarine gate (1.8mm diameter); k : main core; I : cavity (insert); m: shape-forming spme bushing; n: auxilia q core; 0:copper pin; p : stripper plate; q : bolt; r: end stops for stripper plate, p ; s: bead of molding running in stripper plate; r : air blast; u : separate ejector system for spme; 0: bolt head; w : ejector plate; x: shown offset by 60"; y : ejector stroke, 15 mm maximum *i Fig.4 x - Example 33: Three-Plate Injection Mold with Stripping Device for a Precision Magazine 109 Example 33, Three-Plate Injection Mold with Stripping Device for a Precision Magazine Integrated circuits (IC) are generally mounted automatically during production of electronic devices This requires that they be stored in magazines The magazine shown in Fig has an undercut Ushaped groove to hold the ICs and a recessed bottom that is reinforced by transverse ribs Snap fits and mounting holes are located at either end of the magazine The complete runner system is now pulled off the sucker pins (22) and away from the heated sprue bushing (16), dropping out of the mold The springloaded strippers (72) prevent the runner from sticking to the runner plate (5) Shoulder bolts (68) prevent the mold plates from being pulled off the guide pins completely They not, however, serve as a mechanical stop This is found on the molding machine Ejection of the Molded Part In the mold (Figs to ll), the longitudinal axis of the molded part is transverse to the opening direction of the mold The ribbed bottom faces the runner system The cavity is filled via two pinpoint gates from a runner system and a heated sprue bushing (1 6) Mold Operation Parting Line I After a partial opening stroke of approx mm, the spring-loaded bolts (69) cause the gate to shear off The sucker pins (22) hold the runner in the runner plate (5), and the snap fits as well as the mounting holes of the molded part are released by retraction of the slides (33) Mold plates (3) and (4) remain closed during this time Parting Line 11 (mold opening) Parting line I1 (between plates and 4) is opened during M h e r opening of the injection mold This phase of opening is concluded after a distance of 80 mm During this opening motion, the ejector pin (36) is pushed into the eject position by the lever (29) with the aid of a stripper bolt (38) This lifts the hook-shaped detent on the molded part so that it can subsequently be stripped off the mold core Parting Line 111 After a M e r opening stroke of 60 mm, parting line I opens completely through the action of stripper bolt (67) Two M e r stripper bolts (66) engage mold plate (4), pulling the runner plate (5) forward r Mold Figures to 11 Three-plate injection mold with stripping device for a precision magazine 1: movable-side mold base plate; 2: spacer plate; 3, 4: mold plate; 5: m e r plate; 6: cam pin retainer plate; 7: stationay-side mold base plate; , : leader pins; 10, 11, 12, 13, 14, 15: guide bushings; 16: heated spme bushing; 17: movable-side locating ring; 18: insulating plate; 19: junction box for heated spme bushing; 20: locating sleeve; 21: cam pin; 22: sucker pins; 23: spring; 24: mold core; 25, 26: core insert; 27: core; 28: wedge; 29: lever; 30: cavity end insert; 31: guide strip; 32: slide guide; 33: slide; 34: core; 35: articulated head and guide for ejector pin 36; 36: ejector pin; 37: fulcrum for lever 29; 38: stripper bolt; 39: spring-loaded bolt; 40: spring; 41: pivot pin; 42: housing for sensor; 43: sensor; 44: microswitch; 45: housing for microswitch 44; 46: mechanical stop for slide 33; 47: spring; 48: stripper head; 49: base plate for stripping device; 50: bearing support for guide; 51: sheet metal reinforcement; 52: support plate for stripping device; 53: outboard bearing for guide; 54: latch; 55: latch spring; 56: guide block; 57: mechanical limit for inward movement; 58, 59: limit switches; 60: cylinder connection; 61: spring; 62: hydraulic cylinder; 63: linear bearing; 64: guide rod; 65: circlip; 66, 67, 68: stripper bolts; 69: spring-loaded bolt; 70: m e r ejector; 71: adjustment screw; 72: stripper; 73: stationay-side locating ring Figure Precision magazine to hold 50 integrated circuits top: view from above with undercut groove to hold the ICs; bottom; view from below showing the stiffening ribs by which the magazine is pulled off the groove-forming core During the opening sequence of the mold, the stripping device, which is mounted on the moving half of the mold, has moved into the ejection position Only in this position will the limit switch initiate operation of the stripping device During the inward movement, the guide blocks (56) glide under the guide strips (31), the carehlly adjusted latches (54) slide over the transverse stiffening ribs of the molded part and, once the stripping device is hlly inserted, engage behind two of these ribs A limit switch (58) is actuated simultaneously in this position to initiate the stripping operation The molded part is now stripped off the entire length of the mold core (27), which is 162 mm long, and then drops out of the mold Once the stripping device has returned to its starting position, limit switch (59) is actuated and another cycle can start if the infrared mold safety has also cleared the start The infrared mold safety monitors the lower mold half and checks whether the molded part and stripping device have cleared the tool area Only when both conditions have been hlfilled are the machine controls able to initiate another molding cycle 110 Examples ~ Example 33 w m N rN 9119 E I m m - m N m 30 f% E 111 Example 34: 6-Cavity Metal-Powder Injection Mold (MIM) for Transport Fasteners Example 34, 6-Cavity Metal-Powder Injection Mold (MIM) for Transport Fasteners To produce threaded transport fasteners in MIM technology, a standard mold (see also DIN IS0 12165:2002-06, Fig 11) was selected The sixcavity mold is designed mainly with Z standard elements (Hasco) For reasons of wear and temperature, no 1.2344 (X40 Cr Mo V 5-1) hotwork steel hardened to 56-58 HRC was used for the inserts The molded parts are produced from the powdered molding compound, Catamold FN02 [l], [2] Leaving aside the thermoplastic matrix, this material consists of < 0.1% C, 1.9 to 2.2% Ni, the rest being Fe In hardened condition, approx 55 HRC hardness is achieved Several peculiarities have to be considered before processing this compound Standard injection molding machines are, in principle, suited for processing powdered compounds, however the plastifying unit should be as wear-resistant as the mold If “normal” thermoplastics are processed on the same machine, the screw, non-return valve, and cylinder have to be purged (not just “pumped empty”!) after retooling in order to eliminate negative consequences for molded part properties during subsequent sintering Compared to unfilled thermoplastics, this powdered compound has significantly higher temperature and thermal conductivity (approx 10 x greater) In consequence, for example, early gate closing can cause cavity underfilling For this reason, it is necessary to design flow channels generally as wide as possible This is doubly necessary, since melt viscosity and therefore pressure loss, are high A tendency to jetting must also be considered These problematic issues can be kept under control by stepping the injection rate profile It should be observed that the processing window of the powdered compound is significantly smaller compared to standard products, so that considerable experience is required To produce the transport fastenings with a combined molded part weight of x 4.9g and a spme weight of 17g, the following characteristic processing parameters were chosen: Injection rate Injection pressure Cooling time Cycle time 80crn3/s 1500 bar 25 s 38 s Mold This mold cooling system is relatively complex Mold wall temperature is 130 “C In addition to temperature control using pressure water given a temperature of 130 “C, the pressure is approx bar a regulated electrical heating system is provided The outer mold surfaces are completely covered by insulating sheets against heat loss Together with temperature regulation, they provide the thermal balance that is a prime requirement for uniform molded part quality (Fig 1) Manifold and gate dimensions are given in Fig Jetting is not to be expected, since injection is directed against a core Polished venting gaps of approx 0.03mm are ground into the parting planes of the mold After the mold opens, the still ffagile (“green”) parts are demolded gently together with their runners, picked up by a removal device and set down The runner is mechanically separated, regranulated and remixed with the original material for reprocessing without loss of properties It is possible in principle to process powdered compounds on hot-runner systems; however, the increased sophistication and increased equipment requirements often, as in the case at hand, lead to the selection of a standard mold ~ ~ Subsequent Treatment of the Green Parts Subsequent to injection, the green parts are catalytically debindered in a separate operating procedure (the polymer matrix is removed under specified conditions) and sintered Debindering takes place in a nitrogen atmosphere with small traces of gaseous nitric acid at approx 140°C in a drying h a c e The polymer matrix is thereby entirely removed Subsequent sintering is also performed in nitrogen atmosphere at 1200°C Molded parts produced by this method require no M h e r treatment Literature Data sheet Catamold FN02 DiCa 006e Oct 2001, BASF 2.Hickmann, Th., Hemp, E.: Metal Injection Molding MIM: Schnell und yinstig zu F’riizisionsteilen, Kunststoffe 94 (2004) 11, p 62-65 - Next Page 112 ~ , - - Examples L ~ Figure Six-cavity metal-powder injection mold (MIM) for transport fastener ! Example 34 [...]... Plastik & Form, Balingen-Weilstetten,Germany) C) Example 32: Injection Mold for a Polypropylene Container with a Threaded Neck 107 Example 32, Injection Mold for a Polypropylene Container with a Threaded Neck This is the description of a three-plate injection mold for a polypropylene container that does not show in the visual range any witness lines from slides Spme and ejectors are designed for automatic... injection molding position by ejector-plate return pins (12) and buffer pins (16), and so too are the splits, cores and slides by their respective angle pins Example 30: Two-Cavity Injection Mold for a Polypropylene Toy Tennis Racket 101 Example - 30, Two-Cavity Injection Mold for a Polypropylene Toy Tennis Racket The toy tennis racket shown in Fig 1 measures 220mm x 520mm and is made of polypropylene Handle... 30 f% E 111 Example 34: 6-Cavity Metal-Powder Injection Mold (MIM) for Transport Fasteners Example 34, 6-Cavity Metal-Powder Injection Mold (MIM) for Transport Fasteners To produce threaded transport fasteners in MIM technology, a standard mold (see also DIN IS0 12165:2002-06, Fig 11) was selected The sixcavity mold is designed mainly with Z standard elements (Hasco) For reasons of wear and temperature,... 36: handle inserts; 37: ejector bar; 38: guide bushing; 39: screw; 40: ball catch; 41: cooling connection (Courtesy: Plastor p.A., Oradea/Romania) Example 31: Two Injection Molds with Two-step Ejection Process for Housing Components from Polycarbonate 103 Example 31, Two Injection Molds with Two-step Ejection Process for Housing Components from Polycarbonate Injection molds and pressure die-casting molds,... position of the ejector mechanism With this mold, toy rackets can be produced with relatively little mold outlay However, an operator is required because the molded parts are removed manually from the injection molding machine 102 3 Examples ~ Example 30 C 1 2 3 4 B-6 7 a 9 10 11 29 28 12 27 26 25 13 14 24 23 15 16 22 21 20 19 18 17 Figure 2 Two-cavity injection mold for making the racket shown in Fig 1... the Mold The following materials were chosen for the individual parts of the mold: Part-forming inserts: case-hardening steel, case hardened Cavity retainer plate and stripper plate: nitrided annealed steel Mold base: tool steel, unalloyed ~ ~ ~ 108 3 Examples ~ Example 32 Figures 1 to 4 Injection mold for container with threaded neck I, 11: parting lines, TS 1 to 5 temperature control systems a: molded... limit switch (59) is actuated and another cycle can start if the infrared mold safety has also cleared the start The infrared mold safety monitors the lower mold half and checks whether the molded part and stripping device have cleared the tool area Only when both conditions have been hlfilled are the machine controls able to initiate another molding cycle 110 Examples 3 ~ Example 33 3 w m N 1 rN 9119... plate (22) The part-forming surface in the cavity plate and in the handle inserts are produced by spark erosion Operation of the Mold Figure 1 Injection molded, polypropylene toy tennis racket The cavity wall temperature is 50 to 90°C (122 to 194°F) For ejection, the core slides (3) are partly pulled out of the handle bores of the rackets by the angle pins on mold opening (4) The force of the springs... 3 Examples Fig 7 ~ Example 29 Fig 8 Fig 9 Fig 10 Fig 11 9-D J-J K-K G-G L L9 51 H-H 1-1 LO LL 15 16 37 36 36 L1 12 Figure 9 Slide guide for Fig 8 49: guide bar Figure 7 Core guiding for Fig 6 44: punch; 45: guide bar; 46: punch Figure 10 Demolding a slot 30: slide; 41 angle pin; 42: wedge Figure 8 Demolding the rectangular aperture 37: slide; 38: angle pin; 39: locking bolt Figure 11 Slide guide for. .. arrangement in one plane (triangle) avoids this danger Release from the mold is therefore accelerated, since this technique obviates the need for the commonly used but time-consuming method of ejector jolting A coil spring (8) is sticking on the return pin (4); this coil spring enters a boring (9) as the ejector sheets are moving forward This has the following reason: Table 1 lists two forces F1 and